Photographic apparatus and process for controlling the development of individual film units as a function of temperature

ABSTRACT

A camera and a photographic process performed therein in which a viscous photographic processing liquid is distributed in a thin layer between an exposed photosensitive element and another element by moving the elements in superposition through a convergent passage between a pair of juxtaposed pressure-applying members biased toward one another by a substantially constant force. The viscosity of the liquid varies inversely with temperature and the speed of movement of the elements is varied in direct relation to the ambient temperature to insure uniform liquid distribution despite temperature changes. The thickness of the layer of liquid can also be maintained constant despite changes in temperature and viscosity by varying the pressure exerted on the elements by the pressure-applying members, and the camera includes structure for varying the pressure exerted by the pressure-applying members as a function of temperature.

United States Patent Inventor Edwin H. Land Cambridge, Mass. Appl. No878,337 Filed Nov. 20, 1969 ContinuationJn-part of Ser. No. 739,036,June 2i. 1968, abandoned Patented I4,T97l I Assignee PolaroidCorporation Cambridge, Mass.

PI-IOTOGRAPIIIC APPARATUS AND PROCESS FOR CONTROLLING THE DEVELOPMENT OFINDIVIDUAL FILM UNITS AS A FUNCTION OF TEMPERATURE 3,447,437 6/ l 969Tiffany 95/13 Primary Examiner-Samuel S. Matthews AssistantExaminer-Richard L. Moses Attorney.rBrown and Mikulka and Robert E. CorbABSTRACT: A camera and a photographic process performed therein in whicha viscous photographic processing liquid is distributed in a thin layerbetween an exposed photosensitive element and another element by movingthe elements in superposition through a convergent passage between apair of juxtaposed pressure-applying members biased toward one anotherby a substantially constant force. The viscosity of the liquid variesinversely with temperature and the speed of movement of the elements isvaried in direct relation to the ambient temperature to insure uniformliquid distribution despite temperature changes. The thickness of thelayer of liquid can also be maintained constant despite changes intemperature and viscosity by varying the pressure exerted on theelements by the pressure-applying members, and the camera includesstructure for varying the pressure exerted by the pressure-applyingmembers as a function of temperature.

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ATTMNEYS photosensitive sheet material and particularly in portable, l0

hand-held self developing cameras, anexposed photosensitive element istreated in an externally dry process, preferably to produce a positivephotographic print formed by diffusion transfer, by distributing aviscous thixotropic liquid in a thin layer between the photosensitiveelement and another element. The processing liquid may be providedinitially in a rupturable pod ,or container coupled to one of theelements and is distributed between the elements by moving them insuperposition, together with the rupturable container, through aconvergent passage between a pair of juxtaposed pressure-applyingmembers. For optimum results, measured, for example, in terms of imagequality and uniformity as well as reliability and repeatability, andparticularly when the quantity of processing liquid available is limitedto approximately the minimum amount of liquid required, the layer ofprocessing liquid distributed between the elements in contact with thephotosensitive element should be of uniform, predetermined thickness.When the liquid is distributed by moving the elements through aconvergent passage between a pair of pressure-applying members that arefree to move apart from one another and are resiliently biased towardone another, the thickness of the layer of liquid is dependent upon anumber of factors including the pressure exerted by thepressure-applying members, the viscosity of the processing liquid andthe speed of movement of the elements through the passage between thepressure-applying members. The nature and composition of the processingliquid are such that the viscosity of the liquid varies with changes intemperature and, since the thickness of the layer of processing liquidis, in large part, dependent upon the viscosity of the liquid, a problemarises in apparatus such as self-developing cameras which can be carriedand used both indoors and out and are likely to be employed under a widerange of temperature conditions.

An object of the invention is to provide photographic apparatus andmethods of the type described in which the compressive force exerted ona film assemblage by the pressureapplying members is maintainedsubstantially constant and the speed of movement of the film assemblagebetween the pres- I sure-applying members is varied to compensate fortemperature related changes in the viscosity of the processing liquidand thereby provide for distribution of the processing liquid in a layerof predetermined thickness despite changes in ambient temperature andthe viscosity of the liquid.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the process involving the severalsteps and the relation and order of one or more of such steps withrespect to each of the others and the apparatus possessing theconstruction, combination of elements and arrangement of parts which areexemplified in the following detailed disclosure, and the scope of theapplication of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawings wherein:

FlG. l is a somewhat schematic, sectional view of a camera embodying theinvention showing a film assemblage and illustrating the process of theinvention;

FIG. 2 is a perspective view showing components of the camera of FIG. 1;

FIG. 3 is a diagram of an electrical circuit incorporated in the cameraof FIG. 1; and

HO. 4 is a perspective view showing components of the camera of FIG. 1;

The photographic apparatus and process of the invention find particularutility 'in the treatment of photographic film assemblages of the typeincluding all of the materials required to produce a finishedphotographic print, preferably in full color, and including aphotosensitive image-recording clement adapted to be exposed to producean image; a second or image-receiving element adapted to be superposedwith the photosensitive element at least during processing to aid in thedistributionof a viscous processing liquid in contact with the exposedphotosensitive element and preferably to support a visible image formedby diffusion transfer; and a rupturable container of viscous processingliquid adapted, when distributed in contact with the exposedphotosensitive element,

to produce a positive image by a process in which image-formingsubstances are transferred by diffusion from an exposed photosensitivestratum to an image-receptive stratum. Film as- 3 semblages of this typemay take a number of different forms including, for example, separatephotosensitive and second sheets adapted to produce a single print or aplurality of prints; individual film units each including a pair oflayers or sheets coupled with or secured to one another in face to facerel. and adapted to be exposed and processed to produce a single print.The processing liquid may be supplied in a rupturable container coupledwith one or both elements and adapted to be moved together with thesuperposed elements between the pressure-applying members; or it may besupplied from a separate source and dispensed between the elements forsubsequent spreading in a thin layer during movement of the elementsbetween the pressure-applying members.

The camera and process embodying the present invention are especiallyadapted for the treatment of photographic film units of the type shownand described, for example, in the copending U.S. patent application ofEdwin H. Land, Serial No. 622,287, filed March 10, 1967. A typical filmunit of this type includes all of the materials and the reagentsrequired to produce a full color photographic print by a process such asdisclosed in U.S. Pat. No. 2,903,606 issued May 9, 1961, in the name ofHoward G. Rogers. This patent discloses a photosensitive elementincluding a silver halide emulsion and a dye developer, that is, a dyewhich is a silver halide developing agent; a second or image-receivingelement including an image-receptive layer of a dyeable material; and aprocessing liquid in which the dye developer is soluble. Thephotosensitive and image-receiving elements are superposed with theemulsion and image-receptive layers in face-to-face relation and theprocessing liquid is distributed in a uniform layer of predeterminedthickness between and in contact therewith for permeation into thephotosensitive layer where it initiates development of exposed silverhalide. The dye developer is immobilized or precipitated in exposedareas as a consequence of development while in unexposed areas andpartially exposed areas of the emulsion the dye developer remainsunreacted and diffusible thereby providing an imagewise distribution ofunoxidized dye developer which is transferred, at least in part, bydiffusion to the image-receptive layer without altering the imagewisedistribution of the dye developer, to form a reversed or positive colorimage of the developed latent image in the emulsion. Multicolor transferimages are obtained utilizing dye developers, for example, by employingan integral multilayer photosensitive element such as illus trated inFIG. 9 of the 2,983,606 patent, including at least two selectivelysensitized overlying photosensitive strata on a single support. Atypical photosensitive element of this type comprises a support carryinga red sensitive silver halide emulsion stratum, a green sensitive silverhalide emulsion stratum and a blue sensitive silver halide emulsionstratum, each emulsion having associated therewith, respectively, a cyandye respective silver halide emulsion with which they are associated orin a separate layer behind the respective silver halide emulsion.

, Reference is now made to FIG. 1 of the drawings wherein there isillustrated film units of the foregoing type, the thickness of thematerials being exaggerated for'purposes of clarity of illustration.Each film unit, designated 10, comprises a photosensitive orimage-recording sheet 12; a second or image-receiving sheet 14 and arupturable container 16 holding a quantity of processing liquid 18.Sheets 12 and 14 are preferably, although not necessarily, rectangularand coextensive with one another and are arranged in superposedface-toface contact with at least the lateral edges of each sheetaligned with the lateral edges of the other. The two sheets are retainedin superposed relation by a binding element 20 in the form of arectangular sheet larger than either of the photosensitive orimage-receiving sheets and secured to the two sheets at the marginsthereof. Binding element 20 is in the general form of a frame having alarge rectangular opening 22 defining the extent of the exposed area ofthe film unit, surrounded by lateral edge portions and end portions 24and 26. The lateral edge and end portion 24 of binding element 20 areadhered to the lateral and trailing end margins of second sheet 14 andare secured around the edges of the sheets and adhered to the lateraland trailing end margins of photosensitive sheet 12 thereby effectivelybinding the two sheets to one another along three sides thereof. Thepreferred form of film unit shown is adapted to produce a reflectionprint surrounded by a white border and viewed against a white backgroundso that binding element 20 is formed of an opaque white material andcontainer 16 also may be white to provide a more aesthetically pleasingproduct. Second sheet 14 is transparent to enable exposure of thephotosensitive sheet and viewing of the image formed between the sheets.

Container 16 is of the type shown and described in U. S. Pat. No.2,543,l8l and is formed by folding a rectangular blank of fluid and airimpervious sheet material medially and sealing the marginal sections ofthe blank to one another to form a cavity for containing processingliquid 18. The seal between longitudinal marginal sections 28 of thecontainer is weaker than the end seals so that upon application of apredetermined force to the walls of the container in the region of theliquid-filled cavity, there will be generated within the liquidhydraulic pressure sufficient to separate longitudinal marginal sections28 throughout the major portion of their length to form a dischargemouth through which liquid 18 is discharged. Container 16 is attached tosheet 12 and 14 at the leading edges of the sheets preferably with thelongitudinal edge of the container butted against the edges of thesheets with the discharge passage of the container aligned with thefacing surfaces of the sheet.

End portion 26 of binding element 20 is secured to the leading marginaledge of sheet 14 and one marginal section 28 of the container andbinding strip 32 is adhered to the leading marginal edge portion ofsheet 12 and the other marginal section 28 of the container to securethe container to the sheets and cooperates with end portion 26 toprovide a conduit for conducting liquid 18 from the container betweenthe sheets at the leading ends thereof.

The embodiment of the film unit illustrated and described herein isadapted to be exposed and processed to produce a multicolor dye transferimage located between the transparent second sheet 14 on which a dyeablepolymeric layer is supported and an opaque layer located between thetransfer image and the photosensitive medium. This opaque layercomprises the liquid contents 18 of container 16 provided in sufficientquantity to form a layer of predetermined thickness, e.g. of the orderof .004 inch, when distributed uniformly between the sheets over an areaat least coextensive with opening 22 in binding element 20. The quantityof liquid 18 supplied in the container is preferably just sufficient toform a layer of the requisite thickness and extent thereby making itunnecessary to provide means for collecting and retaining excessprocessing liquid and also providing for, minimizing the size of thecontainer and hence, the overall size, complexity and cost of the filmunit. The processing liquid contained in container 16 comprises anaqueous alkaline solution having a pH at which the dye developers aresoluble and diffusible and con-. tains an opacifying agent in a quantitysufficient to mask the dye developers retained in the image-recordinglayer (laminate) subsequent to processing; and a film-forming, viscosityincreasing agent or agents, to facilitate rupture of the container anddistribution of the liquid processing composition and assist inmaintaining the layer of processing composition as a structurally stablelayer tending to bind the sheets to one another.

Subsequent to exposure, film unit 10 is processed by moving the filmunit, with container 16 foremost, relative to and between a pair ofjuxtaposed pressure applying members into and through a convergentpassage between the members for applying compressive pressure first tothe container to eject the fluid contents of the container between thephotosensitive and image-receiving sheets 12 and 14 and then spreadprocessing liquid 18 in a uniform thin layer between the sheets over anarea at least coextensive with opening 22 in binding element 20. Aspreviously noted, the processing liquid in cludes an agent forincreasing the viscosity of the liquid so as to promote the opening ofthe discharge passage of the container throughout substantially itsentire length and facilitate the discharge of the liquid from thecontainer and spreading of the liquid between the sheets. For thispurpose the liquid should be quite viscous and contain the film-formingagent in quantity sufficient to impart a viscosity in excess of 1,000centipoises at a temperature of 20 C. and preferably of the order of1,000 to 200,000 centipoises at said temperature. The processing liquidis preferably thixotropic thereby facilitating complete rupture of thebond between sections 28 of the container comprising the dischargepassage and subsequent spreading of the liquid between the sheets.

A liquid processing composition suitable for incorporation in container16 for use in combination with sheet materials of the type described toproduce a full color transfer image is disclosed in the followingexample:

Water cc. Potassium Hydroxide l 1.2 grams l-lydroxyethyl cellulose 3.4grams (high viscosity) [commercially available from Hercules Powder Co.,Wilmington, DeL, under the trade name Natrasal 250]N-benzyl-a-picolinium l.5 grams bromide Benzotriazole 1.0 grams Titaniumdioxide 40.0 grams The viscosity of an aqueous liquid processingcomposition of the foregoing type varies inversely with temperature,increasing as the temperature is lowered and decreasing as thetemperature is raised.

A pair of film units 10 are illustrated as comprising part of a filmassemblage or pack adapted to be employed in a handheld camera. The filmassemblage or pack includes a box or container 36 adapted to hold aplurality of film units 10 arranged in stacked relation and includes aforward wall 38 provided with an exposure aperture 40 substantiallycoextensive with opening 22 in binding element 20 and a spring andpressure plate assembly 42 for supporting the film units against theforward wall with the forwardmost film unit located in position forexposure in alignment with aperture 40. Box 36includes an end wall 44provided with a narrow slot 46 permitting the movement of the film unitsone at a time from the box through the slot.

A camera of the type adapted to employ the film assemblage for exposingand processing the film units thereof, as illustrated in FIG. 1 ascomprising a housing 48 including a rear section 50 for holding andenclosing container 36, and an intermediate wall having an exposureaperture 52 for locating the forward wall 38 of container 36 in positionfor exposure of the forwardmost film unit supported against wall 38. The

camera includes a forward section 54 for supporting a conventional lens,shutter assembly 56 and providing a light path between the lens and afilm unit positioned for exposure behind exposure aperture 52, andenclosing a mirror 57 located in a plane at 45 with respect to the opticaxis of the lens for reversing the image formed thereby.

The preferred means for spreading the processing liquid in a thin layerbetween the sheets of a film unit includes a pairof juxtaposed memberssuch as cylindrical rolls 58 and 60 cooperating to define a convergentpassage or throat through which the sheets are moved in superpositionwith the container 16 foremost to dispense the liquid contents of thecontainer between the leading end portions of the sheets and thendistribute the liquid from the leading end of the sheets toward thetrailing end thereof. As shown in FIG. 2, roll 60 is mounted forrotation in a substantially fixed position and roll 58 is mounted forrotation about an axis located in the same plane as the axis of roll 60and for movement toward and away from roll 60. The means for mountingroll 58 include a pair of levers 62 pivoted intermediate their ends andeach having means on one end supporting one end of roll 58 for rotationabout its axis. U-shaped springs 64 are provided in engagement with theopposite ends of levers 62 from roll 58, for biasing the levers so as tourge roll 58 toward roll 60. Springs 64 are preferably of a type havinga relatively low spring rate so that the compressive force exerted on afilm assemblage during movement thereof between the rolls remainssubstantially constant despite changes in the separation of the rollsand the deflection of the springs due to variations in the thickness ofthe materials comprising the film unit.

As previously noted, the thickness of the layer of processing liquiddistributed between the elements of a film unit is a function of thecompressive pressure exerted on the film unit by the pressure-applyingmembers, the viscosity of the processing liquid and the speed ofmovement of the film assemblage through the convergent passage betweenthe pressure-applying members. In a hand-held camera such as disclosed,it may be impossible to maintain the camera and film at a constanttemperature so that one of the factors, i.e. liquid viscosity,controlling the liquid spread thickness will constitute an independentvariable while another factor, i.e. pressure, remains substantiallyconstant, so that control over the thickness of the layer of processingliquid distributed within a film unit can be achieved by controlling thethird variable, namely, the speed of movement of the film unit betweenthe pressure-applying rolls.

In the form of camera shown, the film unit is moved between thepressure-applying rolls to spread the processing liquid by advancing theleading end of the film unit into the bite of the rolls and the drivingthe rolls in frictional engagement with the film unit. The means fordriving the rolls comprise an electric motor 66, a source of energy forthe motor such as a battery or batteries 68 and a transmission in theform of a gear train including gears 70, 72, 74, 76 and 78, for drivingroll 60. A gear 80 may be coupled with roll 58 and meshed with gear 78on roll 60 for driving roll 58. The housing includes an opening 82through which film units may be advanced by rolls 58 and 60, and means(not shown) are provided for moving each film unit, following exposurethereof, from exposure position within container 36 through a slot 46into the bite of rolls 58 and 60.

It has been found that the thickness of the layer of processing liquidspread within a film unit varies in direct relation with the speed ofmovement of the film unit between the pressure-applying members so thatthis thickness can be increased by increasing the speed of movement and,conversely, decreased by decreasing the speed of movement. Similarly thethickness of the layer of liquid also varies directly with the viscosityof the processing liquid and hence inversely as the temperature of theprocessing liquid. Accordingly constant liquid spread thickness can beobtained by varying the speed of movement of the film unit directly asthe temperature; that is, by moving the film more slowly at lowertemperatures to compensate for the increased viscosity of the liquid andmoving the film more rapidly at higher temperatures to compensate forthe reduced viscosity of the liquid.

In accordance with the invention, the camera includes means forautomatically sensing the ambient temperature and varying the rate ofrotation of rolls 58 and 60 in accordance with the temperature so as tomaintain constant, a relationship between liquid viscosity and speed ofmovement of the film that will insure spreading of the processing liquidin a layer of predetermined depth even though the temperature andviscosity may vary. Such means may take the form shown, for example, inFIG. 3, and include a temperature responsive resistor such as a negativetemperature coefficient thermistor 84 connected in a conventional bridgecircuit including resistors 86, 88 and 90 coupled with the motor 66 andbattery 68. The values of the resistors comprising the bridge circuitare selected so that the current flowing through the motor will vary asa direct function of the temperature as sensed by thermistor 84. One ofresistors 86, 88 and 90 may be adjustable, making it possible to varythe relationship between tem-' perature and the rate of speed of motor66.

Although the invention has been illustrated in connection with a pair ofpressure-applying members in the form of rolls with the film being movedbetween the rolls by rotation thereof, other forms of pressure-applyingmembers and other means for moving the film through the convergentpassage between the pressure-applying members are known in the art andconsidered to fall within the scope of the invention. Such other formsof pressure-applying members include, for example, nonrotatable membersthat are rigid and biased toward one another, or members dependent fortheir relative mobility and ability to apply pressure, on theirintrinsic resilience. With embodiments of pressure-applying members thatare not rotatable and driven, other means are provided for pushing ordrawing the film between the pressure-applying members, such other meansbeing conventional and known in the art. it is also contemplated thatother temperature responsive means for varying the speed of movement ofthe film between the pressure-applying members fall within the scope ofthe invention. Such other means may include, for example, temperatureresponsive means for switching resistors in and out of the battery-motorcircuit or tapping different terminals of a battery; a temperatureresponsive governor for a suitable electrical or mechanical motor driveor for a manual drive; or a temperature responsive timing mechanism suchas a motor drive with an escapement.

Reference is now made to FIG. 4 of the drawings wherein there isillustrated a structure for varying the pressure exerted on a film unitby the pressure-applying members in response to changes in the in theambient temperature. Although varying the speed of advancement of a filmunit between the rolls in accordance with changes in ambient temperatureshould provide for uniform spread thicknesses despite changes in ambienttemperature, circumstances may become such that it may be advisable tovary the pressure exerted by the rolls on the film unit, also inaccordance with changes in the ambient temperature. Accordingly, inanother embodiment of the invention, provision is made for varyingspread roll pressure as well as speed of advancement so as to maintain apredetermined speed-pressure-temperature relationship and, in this way,provide for spreads of constant uniform thickness despite changes intemperature.

Structures for varying the spread roll pressure in inverse relation toambient temperature are shown and described in the copending UnitedStates patent application of Richard J. Chen, Serial No. 738,954, filedJune 21, 1968. A typical structure for performing this function isillustrated in H6. 4 of the drawings as comprising a pair of juxtaposedpressure-applying members in the form of cylindrical rolls 158 and 160,cooperating to define a convergent passage or throat through which thesheets are moved in superposition with container 16 foremost, todispense the liquid contents of the container between the leadi g endportions of the sheets and then distribute the liquid from the leadingend of the sheets toward the trailing end thereof. As shown in H0. 4,roll 160 is mounted in a substantially fixed position for rotation aboutits axis and roll 158 is mounted for rotation about an axis located inthe same plane as the axis of roll 160 and for movement toward and awayfrom roll 160. Means are provided for biasing roll 158 toward roll 160and in the form shown comprise elongated cantilever springs 162, eachmounted at one end of the camera housing and engaged at its other endwith a shaft (or the journal therefor) on one end of roll 158. Means, tobe described more fully hereinafter, are provided for engaging eachspring 162 intermediate its ends for biasing the free end of each springin the direction of roll 160. The film unit is moved between thepressure-applying rolls to spread the processing liquid by advancing theleading end of the film unit, i.e., the container, into the bite of therolls and driving the rolls in frictional engagement with the film unit.The means for driving the rolls comprise an electric motor 164, a sourceof energy for the motor such as a battery or batteries 166, and atransmission in the form of gear train, gears 168, 170, 172, 174 and 176for driving roll 160. A gear 178 may be coupled with roll 158 and meshedwith gear 176 on roll 160 for driving roll 158.

It is desirable to vary the compressive pressure inversely as totemperature; that is, by applying increased compressive pressure atlower temperatures to compensate for the increased viscosity of theliquid and applying reduced compressive pressure at higher temperaturesto compensate for the reduced viscosity of the liquid. The cameraincludes means for automatically sensing the ambient temperature andresponding by varying the compressive pressure exerted by rolls 158 and160 on the film unit in inverse relation to the temperature so as tomaintain constant a relationship between liquid viscosity andcompressive pressure that will insure spreading of the processing liquidin a layer of predetermined depth even though the temperature andviscosity may vary. Such means may take the form shown, for example, inP16. 4 and include temperature-responsive means for automaticallyvarying the effective length of each of cantilever springs 162 andthereby alter the bias exerted on roll 158 by the cantilever springs. Inthe form shown, these temperature-responsive means comprise a pair ofelongated bars 182, each pivotally mounted at one end adjacent rolls 158and 160 and engaged at its other end 184 with a medial portion of aspring 162 for imparting a bias to the spring. A fixed support member186 is provided for engaging spring 182 adjacent end 184 and supportingend 184 against spring 162. Bars 182 are formed of a material such aszinc-copper and zinc-cadmium alloys, having a relatively highcoefficient of thermal expansion so that the length of each bar willvary with temperature, thereby altering the position of end 184 locatedin engagement with spring 162. The effective length of each spring 162and hence, the force exerted by the spring, is a function of the lengthof the spring between end 184 of bar 182 and roll 158, so that by virtueof the construction shown, an increase in temperature will result in anincrease in length of bars 182 and effective lengths of springs 162,thereby reducing the bias exerted by the springs on roll 158.

It should be noted and appreciated that the novel apparatus and processof the invention enable the performance, over a wide range oftemperature conditions, of a photographic process, particularly adiffusion transfer process, in which a viscous processing liquidcharacterized by a viscosity inversely proportional to temperature isdistributed in a thin layer between a pair of sheetlike elements byadvancing the elements in superposition through a convergent passagebetween a pair of pressure-applying members. With the present invention,it is possible to achieve uniform liquid distribution of a predeterminedthickness automatically and with simple apparatus which lends itself toincorporation in compact, light weight portable cameras; and to employfilm structures including a minimum of excess processing liquid andwhich, as a result, do not require complex, expensive and/or bulkystructures for collecting excess processing liquid. The certainty withwhich uniform liquid distribution of predetermined thickness isobtained, provides for consistent, reliable and high quality results notobtainable with systems wherein the liquid thickness is subject tovariations resulting from changes in temperature.

Since certain changes may be made in the above process and apparatuswithout departing from the scope of the invention herein involved, it isintended that all matter contained in the above description or shown inthe accompanying drawings shall be interpreted as illustrative and notin a limiting sense.

What is claimed is:

l. Photographic processing apparatus for treating an exposedphotosensitive element by distributing a liquid processing agent havinga viscosity which varies with temperature, as a thin layer in contactwith said photosensitive element, said apparatus comprising, incombination:

a pair of pressure members mounted in juxtaposition for relativemovement toward and away from one another and cooperating to provide aconvergent passage between said members through which a photosensitiveelement and a second element are movable in superposition to distributea viscous liquid processing agent in a thin layer between said elements;

biasing means for urging said pressure members toward one another with acontrolled force;

advancement means for moving said elements in superposition through saidconvergent passage between said members; and

temperature-responsive control means coupled with said advancement meansfor sensing the ambient temperature and automatically varying the speedof movement of said elements in direct relation to the ambienttemperature.

2. Photographic processing apparatus as defined in claim 1 wherein saidbiasing means urge said pressure members toward one another with asubstantially constant force.

3. Photographic processing apparatus as defined in claim 2 wherein saidbiasing means include relatively low rate spring means.

4. Photographic processing apparatus as defined in claim 1 wherein saidadvancement means include a drive motor and said control means includemeans for varying the speed of said drive motor in direct relation tothe ambient temperature.

5. Photographic processing apparatus as defined in claim 3 wherein saidmembers comprise a pair of rolls mounted for rotation with their axes ina common plane, said advancement means include drive means for rotatingsaid rolls in engagement with said superposed elements located betweensaid rolls and said control means are coupled with said drive means forvarying the speed of rotation of said rolls in direct relation to theambient temperature.

6. In a photographic process in which a viscous liquid processing agentis distributed in a thin layer between an exposed photosensitive elementand another element superposed therewith, the combination of stepsincluding:

moving said elements in superposition through a convergent passagebetween a pair of juxtaposed pressure-applying members to distribute aviscous liquid agent having a viscosity which varies with temperature,in a thin layer between said elements;

during movement of said elements between said members,

biasing members towards one another into compressive engagement withsaid elements with a controlled force; and

varying the speed of movement of said elements in direct relation to theambient temperature to compensate for temperature-related changes in theviscosity of said liquid agent and thereby distribute said liquid agentin a layer of predetermined thickness. 7. In a photographic process asdefined in claim 6, biasing said members toward one another with asubstantially constant force.

thickening agent. 4

10. A photographic process as defined in claim 9 wherein said liquidprocessing agent is thixotropic and said elements are moved at a speedwithin a range such that said processing agent exhibits thixotrophy.

2. Photographic processing apparatus as defined in claim 1 wherein saidbiasing means urge said pressure members toward one another with asubstantially constant force.
 3. Photographic processing apparatus asdefined in claim 2 wherein said biasing means include relatively lowrate spring means.
 4. Photographic processing apparatus as defined inclaim 1 wherein said advancement means include a drive motor and saidcontrol means include means for varying the speed of said drive motor indirect relation to the ambient temperature.
 5. Photographic processingapparatus as defined in claim 3 wherein said members comprise a pair ofrolls mounted for rotation with their axes in a common plane, saidadvancement means include drive means for rotating said rolls inengagement with said superposed elements located between said rolls andsaid control means are coupled with said drive means for varying thespeed of rotation of said rolls in direct relation to the ambienttemperature.
 6. In a photographic process in which a viscous liquidprocessing agent is distributed in a thin layer between an exposedphotosensitive element and another element superposed therewith, thecombination of steps including: moving said elements in superpositionthrough a convergent passage between a pair of juxtaposedpressure-applying members to distribute a viscous liquid agent having aviscosity which varies with temperature, in a thin layer between saidelements; during movement of said elements between said members, biasingmembers towards one another into compressive engagement with saidelements with a controlled force; and varying the speed of movement ofsaid elements in direct relation to the ambient temperature tocompensate for temperature-related changes in the viscosity of saidliquid agent and thereby distribute said liquid agent in a layer ofpredetermined thickness.
 7. In a photographic process as defined inclaim 6, biasing said members toward one another with a substantiallyconstant force.
 8. A photographic process as defined in claim 6 whereinat least one of said elements is a flexible sheet and compressivepressure is applied to said elements substantially along a lineextending transverse to the direction of movement of said elements.
 9. Aphotographic process as defined in claim 6 wherein said liquidprocessing agent includes water and a polymeric thickening agent.
 10. Aphotographic process as defined in claim 9 wherein said liquidprocessing agent is thixotropic and said elements are moved at a speedwithin a range such that said processing agent exhibits thixotrophy.